KR101461158B1 - Wavelength-tunable external cavity laser module - Google Patents

Abstract

A wavelength tunable external resonant laser module is provided. The wavelength tunable external resonant laser module includes a gain medium for generating light, an optical waveguide coupled to the gain medium and including a thin film heater for controlling the temperature of the Bragg grating and the Bragg grating, and a high frequency transmission medium for transmitting the high frequency signal to the gain medium However, the high-frequency transmission medium controls the operating speed of the light.

Description

[0001] WAVELENGTH-TUNABLE EXTERNAL CAVITY LASER MODULE [0002]

The present invention relates to an external resonant laser module, and more particularly, to a wavelength tunable external resonant laser module.

The present invention is derived from the research carried out as part of the IT growth engine technology development project of the Ministry of Knowledge and Economy [Project Number: 2008-S-008-02, Project Title: Development of FTTH Advanced Optical Component Technology].

Studies on a Wavelength Division Multiplexing (WDM) based passive optical network (PON) have been actively conducted. Hereinafter, the WDM-PON based on wavelength division multiplexing is referred to as a WDM-PON. The WDM-PON can provide voice, data, and broadcasting convergence services.

The WDM-PON is a method in which a communication between a central office (CO) and a subscriber is performed using each wavelength set for each subscriber. Since the dedicated wavelength is used for each subscriber, it is possible to use the other transmission technology such as link rate and frame format for each subscriber or service. I have.

However, since the WDM-PON network multiplexes multiple wavelengths in a single optical fiber using WDM technology, the WDM-PON network requires different light sources as the number of subscribers belonging to one remote node (RN). The production, installation, and management of the light source according to the wavelengths is a great economic burden to both users and operators, which is a great obstacle to the commercialization of WDM-PON. In order to solve this problem, application of a wavelength variable light source device capable of selectively changing the wavelength of a light source has been actively studied.

SUMMARY OF THE INVENTION An object of the present invention is to provide a wavelength tunable external resonant laser module with improved operational characteristics.

A wavelength tunable external resonant laser module according to an embodiment of the present invention includes: a gain medium in which a bias current for generating light is provided; An optical waveguide including a Bragg grating separated from the gain medium to resonate the light and a thin film heater controlling a temperature of the Bragg grating to vary the wavelength of the light that is externally resonated; A high frequency transmission medium for transmitting a high frequency signal to the gain medium; And a package for mounting the gain medium and the optical waveguide. Wherein the gain medium and the optical waveguide are directly coupled to each other and the high frequency transmission medium adds the high frequency signal to the bias current so as to control the light to the same frequency as the high frequency signal, And the current value of the high-frequency signal is controlled to modulate the optical power of the light into a digital signal, and the frequency of the high-frequency signal is the digital signal of 10 gigabits per second or more Wherein the high frequency transmission medium includes a transmission line, a matching resistance portion disposed between the transmission line and the gain medium, and the transmission line and the matching resistance portion may be disposed in the package.

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The high frequency transmission medium according to an exemplary embodiment of the present invention may include a ceramic dielectric and a submount including a metal thin film wire on the ceramic dielectric.

The high frequency transmission medium according to the embodiment of the present invention may include a printed circuit board (PCB).

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The gain medium according to an embodiment of the present invention may include a semiconductor optical amplifier or a laser diode.

The wavelength tunable external resonant laser module according to an embodiment of the present invention further includes a lens interposed between the gain medium and the optical waveguide, wherein the lens can transmit light generated from the gain medium to the optical waveguide.

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The optical waveguide according to an embodiment of the present invention includes a substrate, a cladding layer on the substrate, and a core layer at least partially covered by the cladding layer, wherein the Bragg grating is disposed on the core layer or the cladding layer, A thin film heater may be disposed on the cladding layer.

The optical waveguide according to an embodiment of the present invention may further include a phase adjusting unit, and the phase adjusting unit may be disposed on the cladding layer.

The optical waveguide according to the embodiment of the present invention may further include a low reflection film disposed on the incident surface.

The incident surface of the optical waveguide according to the embodiment of the present invention may be inclined with respect to a vertical plane in the traveling direction of the light.

The core layer and the clad layer according to an embodiment of the present invention may include a polymer.

The core layer and the clad layer according to an embodiment of the present invention may include silica.

The wavelength tunable external resonant laser module according to an embodiment of the present invention may further include a first thermoelectric cooler disposed below the optical waveguide and a thermistor for measuring a temperature of the optical waveguide.

The wavelength tunable external resonant laser module according to an embodiment of the present invention may further include a second thermoelectric cooler for adjusting the temperature of the gain medium and a thermistor for measuring the temperature of the gain medium.

The wavelength tunable external resonant laser module according to an embodiment of the present invention may further include a thermoelectric cooler for controlling the temperature of the optical waveguide and the gain medium, and a thermistor for measuring the temperature.

The wavelength tunable external resonant laser module according to an embodiment of the present invention may further include a photodetector for monitoring the light.

The wavelength tunable external resonant laser module according to an embodiment of the present invention may further include a package on which the gain medium, the optical waveguide, and the high-frequency transmission medium are mounted.

According to an embodiment of the present invention, the wavelength tunable external resonant laser module includes a high frequency transmission medium for transmitting a high frequency signal to a gain medium. The high-frequency transmission medium may control an operation speed of light generated in the gain medium. Therefore, the wavelength tunable external resonant laser module according to the embodiment of the present invention can operate at high speed.

1A is a conceptual diagram for explaining a system using a broadband light source which is one of typical WDM-PON systems.
FIG. 1B is a conceptual diagram for explaining a system using a wavelength variable light source, which is another one of the conventional WDM-PON systems.
FIGS. 2A and 2B are schematic diagrams illustrating a variable wavelength light source. FIG.
3A to 4C are views for explaining a wavelength tunable external resonance laser module according to an embodiment of the present invention.
5 is a view for explaining an optical waveguide of a wavelength tunable external cavity laser module according to an embodiment of the present invention.
6A to 6D are views for explaining the gain medium of the tunable laser resonator module according to an embodiment of the present invention. 6B to 6D are cross-sectional views taken along line BB 'of FIG. 6A.
7A to 7C are views for explaining an optical waveguide and an optical waveguide support unit according to an embodiment of the present invention. FIG. 7A is a top view of a portion where the optical waveguide and the optical waveguide support are combined, FIG. 7B is a left side view of FIG. 7A, and FIG. 7C is a right side view of FIG.
8A is a view for explaining coupling efficiency of light transmitted from a gain medium to an optical waveguide according to an embodiment of the present invention. 8B is a computer simulation graph for explaining light coupling efficiency according to an embodiment of the present invention.
9A is a top view for explaining a tunable laser resonator module according to another embodiment of the present invention. Fig. 9B is an enlarged view of a portion C in Fig. 9A. 10A is a cross-sectional view taken along line II-II 'of FIG. 9A. 10B is an enlarged view of a portion D in FIG. 10C is a computer simulation graph for explaining light coupling efficiency according to an embodiment of the present invention.
11 is a graph illustrating wavelength tuning characteristics according to temperature of an optical waveguide according to an embodiment of the present invention.
12A and 12B are graphs showing transmission characteristics of a high frequency signal according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features, and advantages of the present invention will become more readily apparent from the following description of preferred embodiments with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein but may be embodied in other forms. Rather, the embodiments disclosed herein are provided so that the disclosure can be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

In this specification, when an element is referred to as being on another element, it may be directly formed on another element, or a third element may be interposed therebetween. Further, in the drawings, the thickness of the components is exaggerated for an effective description of the technical content. The same reference numerals denote the same elements throughout the specification.

Embodiments described herein will be described with reference to cross-sectional views and / or plan views that are ideal illustrations of the present invention. In the drawings, the thicknesses of the films and regions are exaggerated for an effective description of the technical content. Thus, the shape of the illustrations can be modified by forming techniques and / or tolerances. Accordingly, the embodiments of the present invention are not limited to the specific shapes shown, but also include changes in shapes that are produced according to the forming process. For example, the etched area shown at right angles may be rounded or may have a shape with a certain curvature. Thus, the regions illustrated in the figures have schematic attributes, and the shapes of the regions illustrated in the figures are intended to illustrate specific types of regions of the elements and are not intended to limit the scope of the invention. Although the terms first, second, third, etc. in the various embodiments of the present disclosure are used to describe various components, these components should not be limited by these terms. These terms have only been used to distinguish one component from another. The embodiments described and exemplified herein also include their complementary embodiments.

The terminology used herein is for the purpose of illustrating embodiments and is not intended to be limiting of the present invention. In the present specification, the singular form includes plural forms unless otherwise specified in the specification. The terms "comprises" and / or "comprising" used in the specification do not exclude the presence or addition of one or more other elements.

1A is a conceptual diagram for explaining a system using a broadband light source which is one of typical WDM-PON systems.

1A, a WDM-PON system 100 mainly includes an optical line terminal (OLT) 110 located at a central office side, an optical network unit or terminal 130, ONU / ONT), and an outdoor node 120 (RN). A feeder optical fiber 117 is connected between the OLT 110 and the RN 120 and a distribution optical fiber 125 is connected between the RN 120 and the ONU 130.

Downstream light is transmitted from a broadband light source (BLS) 112 in the OLT 110 to a first circulator 114, an AWG (Arrayed Waveguide Grating) 113 for a WDM multiplexing / demultiplexing function, Is transmitted to the AWG 123 of the RN 120 via the feeder optical fiber 117 via the transmitter (Reflective Semiconductor Optical Amplifier) 111, the AWG 113 and the first and second circulators 114, The optical signal is transmitted to the ONU optical transmitter 131 and the optical receiver 132 through the optical coupler 133 or the circulator 133 in the ONU 130 via the optical coupler 125.

The upstream light is transmitted in the opposite direction to the upstream downstream light. That is, the upstream light is transmitted from the ONU optical transmitter 131 to the optical coupler 133, the distribution optical fiber 125, the AWG 123 of the RN 120, the feeder optical fiber 117, the second circulator 115 ), The AWG 118, and the optical receiver 116 for OLT.

The advantage of this method is that OLT side light source is also used in ONU, so there is no need to secure a separate light source at the subscriber side, and it is possible to decorate a colorless system. However, since RSOA is used as an amplification and modulation medium, it is recognized as a method that is difficult to use in a 10 Gbps system because of a speed limitation.

FIG. 1B is a conceptual diagram for explaining a system using a wavelength variable light source, which is another one of the conventional WDM-PON systems.

1B, the WDM-PON system 200 includes an optical line terminal (OLT) 210 located on a central office side, an optical network unit or terminal (ONU) 230 on a subscriber side, / ONT), and an outdoor node 220 (RN). A feeder optical fiber 217 is connected between the OLT 210 and the RN 220 and a distribution optical fiber 225 is connected between the RN 220 and the ONU 230.

The downstream light is transmitted from the wavelength tunable light source 211 of the base station transmitting terminal 210 through the AWG 214, the feeder optical fiber 217, the AWG 223, the distribution optical fiber 225, the WDM filter 233, To the light receiver section (232). The upstream light travels in the direction opposite to the upstream downstream light and is transmitted to the light receiving unit 212 of the base station transmitting terminal 210.

 Unlike FIG. 1A, the wavelength tunable light sources 211 and 231 are used for the base station transmitter 210 and the subscriber network 230, respectively, in order to construct a system having no wavelength dependency. Although there is a limitation that each of the base station transmitting terminal 210 and the subscriber network 230 is required to have a light source, it is advantageous in that it can realize high performance in terms of speed since it uses a laser. The key to implementing such a system depends on the ability to create reliable wavelength tunable light sources at low cost.

FIGS. 2A and 2B are schematic diagrams illustrating a variable wavelength light source. FIG.

Referring to FIG. 2A, a single variable component of each wavelength variable light source is shown. The wavelength tunable light source includes a second Bragg region 340 having a first Bragg region 310 having a first Bragg grating 317, a gain medium 320, a phase control region 330 and a second Bragg grating 307, . The first electrode 305 and the second electrode 302 are electrodes for supplying a gain current and the first electrode 305 and the third electrode 303 are electrodes for supplying a phase current, 305 and the fourth electrode 301 can change the refractive index of the first Bragg region 310 to supply a current for adjusting the Bragg wavelength. The first electrode 305 and the fifth electrode 304 may change the refractive index of the second Bragg region 340 to supply a current for adjusting the Bragg wavelength.

If the components having different functions are integrated into one device, the uniformity of the devices may be a problem due to the characteristics of the forming process. A mirror surface such as a distributed Bragg reflector (DBR) is attached to the front and rear positions of the gain medium 320 and the phase control region 330 is integrated. The optical amplifier is also integrated to improve the output power. Since each functional part uses a different composition medium, various problems such as internal reflection and absorption at the interface are liable to occur when they are integrated through material growth and etching processes. Furthermore, in order to control each part of various devices separately, it is necessary to automate the measurement of characteristics. Even if the measurement is automated, it takes a long time to find a specific wavelength using various combinations of currents. As a result, the complexity of the control unit can not be avoided even after the module is manufactured.

2B shows a hybrid structure in which a gain medium 350 and an external grating 360 are packaged to fabricate a laser. A single element used as the gain medium 350 and a separate external Bragg grating 360 capable of controlling the reflection and the wavelength are packaged to manufacture an external resonator laser. Each of the parts is separately manufactured. The yield can be increased and fabrication using the conventional optical device packaging method is advantageous. The outer Bragg grating 360 is fabricated using a compound semiconductor, silica or polymer material.

3A to 4C are views for explaining a wavelength tunable external resonance laser module according to an embodiment of the present invention. 3A is a top view of a tunable external resonant laser module. FIG. 3B is an enlarged view of a portion A in FIG. 3A. FIG. 4B is a cross-sectional view taken along line I-I 'of FIG. 3A. Fig. 4C is an enlarged view of part B of Fig. 4B.

3A to 4C, the wavelength tunable external resonant laser module 1000 includes a gain medium 500 for generating and amplifying light, an optical waveguide 400 for forming a mirror surface in combination with the gain medium 500, And a high frequency transmission medium (600) for transmitting a high frequency signal to the gain medium (500). The high-frequency transmission medium 600 can control the operation speed of the generated light. Specifically, when a bias current is applied to the gain medium 500, light is generated and amplified. When the bias current is greater than a threshold value, the gain medium 500 is formed by the gain medium 500 and the optical waveguide 400 Lasing occurs in the mirror plane. A high frequency signal transmitted by the high frequency transmission medium 600 is added to the bias current so that the magnitude of the optical power generated in the laser is adjusted. The operating speed of the light can be determined by the frequency of the high-frequency signal. Here, the operating speed of the optical signal can be understood as a repetition rate (bit per second) of a digital signal or an analog signal.

The high-frequency transmission medium 600 may adjust the optical power of the optical signal. Further, the high-frequency signal may be modulated into a digital signal defined by the optical power. In detail, the current value of the high-frequency signal transmitted by the high-frequency transmission medium 600 may be adjusted so that a relatively high optical power above a threshold current is modulated into a digital signal of 1, and a relatively low optical power of 0 have. Such a digital signal may have a value of 10 Gbps (Giga bit per second) or more.

The high frequency transmission medium 600 may be a printed circuit board or a submount. The printed circuit board or submount may include a conductive metal foil wire 610, a dielectric 620, and a matching resistor 630. When the high-frequency transmission medium 600 is a printed circuit board, the dielectric 620 may include an epoxy resin or a phenolic resin. If the high frequency transmission medium 600 is a submount, the dielectric 620 may comprise a ceramic dielectric. The matching resistance unit 630 may be added to the resistance value of the gain medium 500 to control the signal transmission through the high frequency transmission medium 600 to be good. The total resistance including the gain medium 500 may be controlled by the matching resistance unit 630 to be 25, 50, 75? Or the like which is the same as the internal resistance of the transmission signal source. The metal foil wire 610 on the high frequency transmission medium 600 may include a microstrip line or a coplanar waveguide (CPW), and may be combined with the dielectric to form a transmission line.

The gain medium 500, the optical waveguide 400, and the high-frequency transmission medium 600 may be all mounted on the package 710. The package 710 may be a package such as a butterfly, a mini DIL, a mini flat, or a Transmitter Optical Sub-assembly (TOSA). The package 710 may include a lead frame 705 that transmits an external electrical signal. The high frequency transmission medium 600 may transmit a high frequency signal transmitted through the high frequency connector 730 to the gain medium 500.

The gain medium 500 and the optical waveguide 400 can be optically coupled directly to each other without the intervention of a lens. According to the direct coupling method, the wavelength tunable external resonant laser module according to the embodiment of the present invention can reduce the resonator length in which the laser signal is generated, and thus the bandwidth can be secured easily. That is, when the frequency operation characteristic is measured, a resonance peak corresponding to the length of the external resonator is generated. The resonance peak is transmitted to the higher frequency region by implementing the short resonator, thereby reducing the bandwidth reduction effect caused by the resonance peak, Can be advantageous.

The optical waveguide 400 may be coupled to the package 710 directly or through a separate optical waveguide support structure 740. When the optical waveguide 400 is directly coupled to the package 710, the metal support for Welding 720 and the optical waveguide support 740 may be unnecessary. In this case, one of the gain medium 500 or the optical waveguide 400 is fixed in advance and the other is fixed in a range of 1 to 50 mu m by a passive alignment method such as flip chip bonding Lt; / RTI >

The optical waveguide 400 may be coupled to a separate optical waveguide support 740. The optical waveguide supporter 740 and the package 710 may be optically coupled by an active alignment method using a metal support 720 for Welding.

A first thermoelectric cooler 405 may be disposed below the optical waveguide 400. The first thermoelectric cooler 405 can adjust the temperature of the optical waveguide 400 to a specific temperature. The gain medium 500 may be disposed above the first thermoelectric cooler 405 or a separate second thermoelectric cooler 570. The first thermoelectric cooler 405 or the second thermoelectric cooler 570 may adjust the temperature of the gain medium 500 to a specific temperature. A structural support 590 may be disposed between the first thermoelectric cooler 405 or a separate second thermoelectric cooler 570 and the gain medium 500. The structure supporting portion 590 may include a silicon or compound semiconductor substrate having a pattern for device alignment formed thereon, or super usable stainless steel (SUS) having excellent workability. A thermistor 585 for temperature measurement of the gain medium 500 may be disposed on the structure support 590. A photodetector 575 may be disposed on the structural support 590 to monitor the optical signal of the gain medium 500. The photodetector 575 may include a photodiode.

The soldering metal support 720 may form a heat dissipation path of the optical waveguide 400. In a state where the package is assembled, a solder or a silver component epoxy or the like is applied to the joint portion, .

The optical waveguide 400 may be coupled to a separate optical waveguide support 740. The optical waveguide supporter 740 and the package 710 may be optically coupled by an active alignment method using a metal support 720 for Welding. The metal support for welding 720 may be used to emit heat of the optical waveguide 400. Alternatively, a heat release path can be formed by using a solder, a silver component epoxy, or the like while the package is assembled.

5 is a view for explaining an optical waveguide 400 of a wavelength tunable external resonance laser module according to an embodiment of the present invention.

Referring to FIG. 5, the optical waveguide 400 may be a planar lightwave circuit (PLC). The optical waveguide 400 includes an optical waveguide formed of a core 401 and a cladding layer 402 on a silicon or compound semiconductor substrate 403. The cladding layer 402 may cover at least a part of the core 401. The core 401 and the cladding layer 402 may comprise polymeric and silica materials. The thermo-optic coefficient of the polymer and silica may be from -9.9 X 10 ^-4 / K to -0.5 X 10 ^-4 / K. The refractive index of the core 401 should be higher than that of the cladding layer 402. The core 401 or the cladding layer 402 may include a Bragg grating 410. The Bragg grating 410 may be formed by a dry or wet etching method and may reflect a specific wavelength. When the core 401 is a polymer material, the thermo-optic coefficient may be higher than that of silica, and the refractive index may be changed in proportion to the thermo-optic coefficient due to temperature control from the outside. A change in the refractive index of the core 401 may cause a change in the reflected wavelength.

For example, when the core 401 has a thermo-optic coefficient of ^-3 × 10 ^-4 / K and a refractive index of 1.4, the wavelength is changed in the range of 1530 to 1565 nm through a temperature change of about 105 K . In order to adjust the temperature of the core 401, a thin film heater 404 made of a metal is deposited, and a current is applied to the thin film heater 404 to control the temperature. Specifically, when a current is injected into the thin film heater 404, the temperature of the core 401 is increased, the refractive index of the core 401 is decreased due to the thermo-optic effect, and the effective period of the Bragg grating 410 is The output light wavelength of the external resonance laser can be changed toward the short wavelength side. The center wavelength of the reflection band of the Bragg grating 410 can be adjusted to 30 nm or more by the thin film heater 404. Thus, the center wavelength of the laser beam oscillated by the tunable external resonance laser module can be adjusted to 30 nm or more. In order to stabilize the specific wavelength, the phase adjusting unit 406 is deposited together with the thin film heater 404 so that the change of the fine phase can be controlled by the change of the temperature by the current injection and the change of the refractive index. The Bragg grating 410 may be periodically arranged in the core 401 and connected in series. The Bragg grating 410 may have an order of 1, 3, 5, or 7 orders.

6A to 6D are diagrams for explaining the gain medium 500 of the tunable laser resonator module according to an embodiment of the present invention. 6B, 6C and 6D are cross-sectional views taken along the line B-B 'in FIG. 6A, respectively, and show other types of active waveguide regions.

The gain medium 500 may be a general optical amplifier, a reflective optical amplifier (RSOA), a laser diode, or the like. Hereinafter, the case where the gain medium 500 is a reflection type optical amplifier (RSOA) will be described.

Referring to FIG. 6A, the gain medium 500 may include a passive waveguide region 512 in addition to the active waveguide region 511. The active waveguide 521 can gain gain by current injection, and the passive waveguide 522 can serve as a waveguide without gain. The generated light is transmitted to the mirror surface formed by the optical waveguide 400 via the line A-A '. First, the feedback light from the optical waveguide 400 is input again through the low reflection coating low reflection film 514, the gain is obtained from the active waveguide 521 through the passive waveguide 522, And is reflected by the ghosted high reflection film 513. This process is repeated in the inside, and the laser beam is partially output from the reflection film to be used as a signal.

The internal reflection directly input to the gain medium through the inner low-reflectance film of the gain medium 500 adversely affects the laser characteristics of the external resonator structure. Therefore, in order to further reduce the reflectance, and a passive waveguide 522 inclined at &thetas;. In this case, most of the light directly reflected by the low reflection film by the Snell's law passes out of the waveguide. The passive waveguide 522 may include a spot size converter (SSC) that increases the optical coupling efficiency by making the optical mode and shape of the optical fiber similar. The implementation of the mode size converter changes the mode size by tapering or increasing the width of the end of the passive waveguide 522. In the case of the direct coupling between the gain medium 500 and the optical waveguide 400, it is difficult to obtain high optical coupling efficiency as compared with the case of using a lens because of the difference in mode size and shape between two waveguide elements. The optical coupling efficiency can be obtained.

In order for the laser of the external resonator structure to operate at a high frequency of 10 Gbps or more, the self-operating frequency of the gain medium 500 should have a larger value. For example, when Fabry-Perot Laser Diode (FPLD) is fabricated using a gain medium 500, when the operating frequency of the device shows a 10 Gbps operating characteristic over the operating current range, If a laser with an external resonance structure is made, there is a possibility that the frequency characteristic of 10 Gbps is shown. Such a laser structure capable of high-frequency operation includes a shallow ridge structure and a deep ridge structure laser, a buried ridge structure laser, an Fe-doped laser, have.

The active waveguide region 511 includes a p-type electrode 523 and an n-type electrode 557 to which current is injected, an active waveguide 521, an active waveguide 521, And an ohmic layer 554 for reducing the resistance between the upper cladding layer 553 and the p-type electrode 523. The upper cladding layer 553 and the lower cladding layer 551 cover the upper cladding layer 553 and the p- A buried heterostructure having p-InP / n-InP / p-InP (561/562/553) current blocking layers may be disposed on both sides of the active waveguide 521. The buried heterostructure is limited in operation in the high frequency region by a large parasitic capacitance component. Accordingly, as shown in FIG. 6B, the trench 528 is formed close to the active waveguide and the dielectric thin film 529 covering the trench 528 is formed, thereby reducing the parasitic capacitance.

The active waveguide 521 includes a gain medium layer 521b. The active waveguide 521 may further include upper and lower SCH (Separate Confinement Heterostructure) layers 521c and 521a that effectively bind light and gain materials such as bulk, quantum well, quantum wire, and quantum dot. The upper cladding layer 553 may be formed of p-InP, the lower cladding layer 551 may be formed of n-InP, and the upper ohmic layer 554 may be formed of p + -InGaAs. The lower ohmic layer (not shown) may be formed of n + InGaAs. Here, p +, n +, etc. mean a case where doping is performed at 1 × 10 ¹⁸ / cm 3 or more.

Referring to FIG. 6C, the portion excluding the current blocking layer is substantially the same as that of FIG. 6B, except for which portion of the active waveguide is formed as a ridge. The structure shown in FIG. 6C may be divided into a shallow ridge structure. The description of the overlapping description with reference to FIG. 6B will be omitted for the sake of brevity. an n-type electrode 857 is formed on the upper cladding layer 851. The lower cladding layer 851 on the n-type electrode 857, the active waveguide 821 on the lower cladding layer 851, the upper cladding layer 853 on the active waveguide 821, An ohmic layer 854 on the ohmic layer 853 and a p-type electrode 823 on the ohmic layer 854 are disposed. The active waveguide 821 may be formed of a gain medium layer 821b and upper and lower SCH layers 821c and 821a. An upper ohmic layer 854 is formed between the upper cladding layer 853 and the p-type electrode 823 and a dielectric layer 829 disposed between the upper cladding layer 853 and the p- A mid layer 827 is disposed.

Referring to FIG. 6D, the portion except for the current blocking layer is substantially the same as in FIG. 6B, and only the portion of the active waveguide which forms the ridge is different. The structure shown in FIG. 6D can be divided into a deep ridge structure. The description of the overlapping description with reference to FIG. 6B will be omitted for the sake of brevity.

an n-type electrode 957, a lower cladding layer 951 on the n-type electrode 957, an active waveguide 921 on the lower cladding layer 951, an upper cladding layer 953 on the active waveguide 921, And a p-type electrode 923 on the p-type electrode 953 is formed. The active waveguide 921 may be formed of a gain medium layer 921b and upper and lower SCH layers 921c and 921a. A silicon oxide film or a silicon nitride film 929 may be formed along both sides of the upper cladding layer 953 and the upper surface of the active waveguide 921. A polyimide layer 927 may be formed between the p-type electrode 923 and the active waveguide 921 while covering the silicon oxide film or the silicon nitride film 929.

FIGS. 7A to 7C are views for explaining the optical waveguide 400 and the optical waveguide support unit 740 in the case of using a separate optical waveguide support unit according to an embodiment of the present invention. 7A is a top view of a portion where the optical waveguide 400 and the optical waveguide supporter 740 are combined, FIG. 7B is a left side view of FIG. 7A, and FIG. 7C is a right side view.

7A to 7C, the optical waveguide 400 may be fixed to the optical waveguide support portion 740 in a state in which the optical waveguide 400 is tilted in the horizontal direction. This is because the ends are etched at a certain angle in order to minimize the direct reflection of the light from the incident surface of the optical waveguide 400 to the gain medium 500. The Snell's law allows the input / This is to compensate for the angular deflection. This is a principle similar to breaking the passive waveguide of the gain medium 500. That is, unwanted reflection from the incident surface of the optical waveguide 400 is prevented to prevent deterioration of the laser characteristics of the external resonator structure. In addition, the optical waveguide 400 may further include a low reflection film 420 disposed on an incident surface. The surface of the optical waveguide 400 may have a reflectance of 1% or less only by the low reflection film 420. The first thermoelectric cooler 405 described above may be disposed below the optical waveguide 400. A temperature sensor (not shown) for monitoring the temperature of the optical waveguide 400 adjacent to the optical waveguide 400 may be further disposed. The optical waveguide supporter 740 may include a hole 745 to which an optical fiber (not shown) capable of extracting input and output light of the optical waveguide 400 may be coupled.

8A is a view for explaining a method of coupling light transmitted from the gain medium 500 to the optical waveguide 400 according to an embodiment of the present invention. 8B is a computer simulation graph for explaining light coupling efficiency according to an embodiment of the present invention.

Referring to FIG. 8A, the gain medium 500 includes an active waveguide 521 and a passive waveguide 522. As described above, the passive waveguide 522 is inclined at a certain angle from the active waveguide 521 in order to reduce the size of light reflected directly from the optical output surface of the gain medium 500 to the active waveguide. The light thus output is not perpendicular to the output surface but is output at an angle with a condition satisfying Snell's law. The gain medium 500 is arranged so as to be inclined by the angle? 1 such that the light is perpendicularly incident on the optical waveguide 400. [

Meanwhile, as described above, the optical waveguide 400 is fixed to the optical waveguide supporter 740 by a certain angle? 2. In other words, the waveguide of the optical waveguide 400 may be inclined by? 2 with the incident angle of the light. This is because the incident surface of the optical waveguide 400 is cut at a certain angle or the groove 430 is formed on the incident surface in order to minimize the reflection of light on the incident surface of the optical waveguide 400, The surface has an angle? 3 with respect to the normal direction of the waveguide, so that the directly reflected light can not directly enter the gain medium 500. The gain medium 500 may be assembled in the vicinity of the groove 430.

Referring to FIG. 8B, coupling efficiency is shown when the angle? 2 described in FIG. 8A has an angle satisfying Snell's law and when the angle? 2 is zero. In the horizontal axis, L represents the distance between the gain medium and the optical waveguide. It can be seen that the coupling efficiency of light is higher when the angle &thetas; 2 is an angle satisfying Snell's law. Specifically, the coupling efficiency is as high as about 10% as compared with the case where the angle [theta] 2 is zero. If the waveguide shape on the optical waveguide 400 has a shape similar to that of the waveguide on the gain medium and is formed with an angle to follow the optical path according to Snell's law, the gain medium and the optical waveguide can be arranged to face horizontally , The distance between the two can be minimized since the restriction of the approach distance by the structural inclination can be eliminated.

The wavelength tunable external resonant laser module according to the embodiment of the present invention can tunes the wavelength by the thin film heater 404 while maintaining the specific temperature regardless of the temperature change of the external environment by the first thermoelectric cooler 405 . At the same time, high-frequency operation can be performed by the high-frequency transmission medium 600.

9A to 10B, the wavelength tunable external resonant laser module 2000 includes a gain medium 2500 for generating and amplifying light, an optical waveguide 2400 for optically coupling with the gain medium 2500 to form a mirror surface, And a high frequency transmission medium 2600 for transmitting a high frequency signal to the gain medium 2500. The high frequency transmission medium 2600 can control the operation speed of the generated light. More specifically, when a bias current is applied to the gain medium 2500, light is generated and amplified. When the bias current is greater than a threshold value, the gain medium 2500 and the optical waveguide 2400 Lasing occurs in the mirror plane. A high frequency signal transmitted by the high frequency transmission medium 2600 is added to the bias current so that the magnitude of the optical power generated in the laser is adjusted. The operating speed of the light can be determined by the frequency of the high-frequency signal. Here, the operating speed of the optical signal can be understood as a repetition rate (bit per second) of a digital signal or an analog signal.

The high frequency transmission medium 2600 may adjust the optical power of the optical signal. Further, the high-frequency signal may be modulated into a digital signal defined by the optical power. Specifically, by adjusting the current value of a high-frequency signal transmitted by the high-frequency transmission medium 2600, a relatively high optical power at a threshold current or higher is modulated into a digital signal defined as 1, and a relatively low optical power is defined as 0 . Such a digital signal may have a value of 10 Gbps (Giga bit per second) or more.

The high frequency transmission medium 2600 may be a printed circuit board or a submount. The printed circuit board or submount may include a conductive metal foil wire 2610, a dielectric 2620, and a matching resistor 2630. If the high frequency transmission medium 2600 is a printed circuit board, the dielectric 2620 may include an epoxy resin or a phenolic resin. If the high frequency transmission medium 2600 is a submount, the dielectric 2620 may comprise a ceramic dielectric. The matching resistance portion 2630 may be added to the resistance value of the gain medium 2500 to adjust the signal transmission through the high frequency transmission medium 2600 to be good. The total resistance including the gain medium 2500 by the matching resistance unit 2630 can be adjusted to 25, 50, 75? Or the like which is the same as the internal resistance of the transmission signal source. The metal foil wire 2610 on the high frequency transmission medium 2600 may include a microstrip line or a coplanar waveguide (CPW), and may be combined with the dielectric to form a transmission line.

The gain medium 2500, the optical waveguide 2400 and the high-frequency transmission medium 2600 may be all packaged in a package 2710. The package 2710 may be a package such as a butterfly, a mini DIL, a mini flat, a Transmitter Optical Sub-assembly (TOSA), a TO (Transistor Outline) . The package 2710 may include a lead frame 2705 for transmitting an external electrical signal. The high frequency transmission medium 2600 may transmit a high frequency signal transmitted through the high frequency connector 2730 to the gain medium 2500.

The optical waveguide 2400 may be coupled to the package 2710 through a separate optical waveguide support structure 2740. In this case, one of the gain medium 2500 or the optical waveguide 2400 is preliminarily fixed to the package 2710 and the other is applied to the package 2710 by using a metal support 2720 for welding, alignment and then fixed by welding.

A first thermoelectric cooler 2405 may be disposed below the optical waveguide 2400. The first thermoelectric cooler 2405 can adjust the temperature of the optical waveguide 2400 to a specific temperature. The gain medium 2500 may be disposed on a separate second thermoelectric cooler 2570. The second thermoelectric cooler 2570 may adjust the temperature of the gain medium 2500 to a specific temperature. A structural support 2590 may be disposed between the second thermoelectric cooler 2570 and the gain medium 2500. The structure supporting portion 2590 may include a silicon or compound semiconductor substrate in which a pattern for device alignment is formed, or super usable stainless steel (SUS) having excellent workability. A thermistor 2585 for temperature measurement of the gain medium 2500 may be disposed on the structure support 2590. A photodetector 2575 may be disposed on the structural support 2590 to monitor the optical signal of the gain medium 2500. The photodetector 2575 may include a photodiode.

The soldering metal support 2720 may form a heat dissipation path of the optical waveguide 2400. When the package is assembled, a solder or a silver component epoxy or the like is applied to the junction to provide a heat dissipation path .

The lens 2800 may be interposed between the gain medium 2500 and the optical waveguide 2400, unlike the embodiment of the present invention. The lens 2800 can optically couple the gain medium 2500 and the optical waveguide 2400. That is, the size and shape of the gain medium mode can be controlled by the action of the lens 2800, thereby improving the optical coupling efficiency. A low reflection film (not shown) may be disposed on both sides of the lens 2800 to further improve the optical coupling efficiency. The lens 2800 may be mounted in the package 2710 together with the gain medium 2500 and the optical waveguide 2400.

Referring to FIG. 10C, coupling efficiency due to lens intervention is exemplified when the angle? 2 described in FIG. 8A is 0 and the angle? 2 has an angle satisfying Snell's law. In the horizontal axis, L represents the distance between the gain medium and the optical waveguide. It can be seen that the coupling efficiency of light is higher when the angle &thetas; 2 is an angle satisfying Snell's law. Specifically, it shows a coupling efficiency of about 2/3 level as compared with the case where the angle? 2 is zero. Comparing the maximum optical coupling efficiency, the coupling efficiency is close to 100% in theory, which is 1.5 times higher than that of the direct coupling method, which is advantageous in terms of static laser characteristics such as output optical power. However, due to the lens intervention, the total length of the resonator increases, so that a resonance peak is likely to occur within the frequency range to be used, which may result in bandwidth reduction.

11 is a graph illustrating wavelength tuning characteristics according to temperature of an optical waveguide according to an embodiment of the present invention.

In Fig. 11, the horizontal axis indicates the wavelength?, And the vertical axis indicates the optical power P (dBm). And the wavelength is varied according to the temperature of the optical waveguide 400. FIG. Side Mode Suppression Ratio (SMSR) is more than 30dBm. Specifically, after the temperature of the optical waveguide 400 is fixed to a specific temperature by using the first thermoelectric cooler 405, the temperature of the waveguide part of the optical waveguide is adjusted by heating the thin film heater 404, have.

12A and 12B are graphs showing transmission characteristics of a high frequency signal according to an embodiment of the present invention.

12A, the ordinate indicates the reflection coefficient S11, and the abscissa indicates the frequency (GHz). It can be seen that the high frequency signal is transmitted to the laser well up to 10 GHz based on the reflection coefficient of -10 dB and it is also possible to obtain higher frequency characteristics by adjusting the matching resistance and the like.

12B, the vertical axis represents the operating bandwidth S21 of the laser, and the horizontal axis represents the frequency (GHz). It can be seen that the -3dB bandwidth is 10 GHz and that high-speed operation is possible over 10 Gbps.

400: optical waveguide 500: gain medium
600: high frequency transmission medium 610: metal foil wire
710: Package

Claims (19)

A gain medium in which a bias current for generating light is provided;
An optical waveguide including a Bragg grating separated from the gain medium to resonate the light and a thin film heater controlling a temperature of the Bragg grating to vary the wavelength of the light that is externally resonated;
A high frequency transmission medium for transmitting a high frequency signal to the gain medium; And
And a package for mounting the gain medium and the optical waveguide,
Wherein the gain medium and the optical waveguide are directly optically coupled to each other,
Wherein the high frequency transmission medium adds the high frequency signal to the bias current so as to control the light to the same frequency as the high frequency signal,
Wherein the gain medium generates the light corresponding to the bias current added to the high frequency signal,
Wherein the current value of the high-frequency signal is controlled to modulate the optical power of the light into a digital signal,
The frequency of the high-frequency signal is set to the digital signal of 10 gigabits per second or more,
Wherein the high frequency transmission medium includes a transmission line, a matching resistor disposed between the transmission line and the gain medium,
Wherein the transmission line and the matching resistor are disposed in the package. delete delete The method according to claim 1,
Wherein the high frequency transmission medium includes a ceramic dielectric, the transmission line formed of a metal thin film on the ceramic dielectric, and a submount having the transmission line. The method according to claim 1,
Wherein the high frequency transmission medium comprises a printed circuit board (PCB). delete The method according to claim 1,
Wherein the gain medium comprises a semiconductor optical amplifier or a laser diode. delete The method according to claim 1,
Further comprising a lens interposed between the gain medium and the optical waveguide,
Wherein the lens transmits the light between the gain medium and the optical waveguide. The method according to claim 1,
The optical waveguide includes:
A cladding layer on the substrate; And
Further comprising a core layer at least partially covered by the cladding layer,
Wherein the Bragg grating is disposed on the core layer or the cladding layer, and the thin film heater is disposed on the cladding layer. The method of claim 10,
Wherein the optical waveguide further comprises a phase adjusting section disposed on the cladding layer. The method of claim 10,
Wherein the optical waveguide further comprises a low reflection film disposed on an incident surface. The method of claim 10,
Wherein an incident surface of the optical waveguide is inclined with respect to a vertical plane in the traveling direction of the light. The method of claim 10,
Wherein the core layer and the cladding layer comprise a polymer. The method of claim 10,
Wherein the core layer and the cladding layer comprise silica. The method of claim 10,
And a first thermoelectric cooler disposed below the optical waveguide. The method according to claim 1,
A second thermoelectric cooler for adjusting the temperature of the gain medium; And
And a thermistor for measuring the temperature of the gain medium. The method according to claim 1,
And a photodetector for monitoring the light. The method according to claim 1,
And a package on which the gain medium, the optical waveguide, and the high-frequency transmission medium are mounted.

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